Description of Project Exposure to hepatitis C virus can lead to an acute, self-resolving infection but in most cases acute infection will progress to a chronic state characterized by persistent viral RNA replication. The proceses that effect acute or chronic infection outcome after HCV and HCV-HIV exposure have not been defined. Our studies indicate that innate intracellular antiviral defenses can control HCV RNA replication through pathogen signaling pathways of interferon regulatory factor (IRF) activation. These pathways are triggered through distinct processes by retinoic acid inducible gene-l, Toll-like receptor (TLR)3, and protein kinase R (PKR) to induce IRF transactivation of type I interferon (IFN) production and the expression of target genes that control virus infection. Our in vitro studies have shown that HCV can overcome this host response through the actions of the NS3/4A protease and the NS5A protein to respectively block signaling by RIG-I and TLR3 pathways, and to inhibit PKR signaling actions. This project will investigate the hypothesis that HCV regulation of innate intracellular defenses controls the outcome of infection. Our Specific Aims are designed to identify the virus/host interface that controls the host response to infection. Our studies will feature the use of the chimeric mouse and HCV replicon culture systems to define the viral and host parameters that impart and regulate innate antiviral defenses against HCV and HCV/HIV co-infection in vivo and antiviral effector actions in vitro. Aim 1 studies will define the virus-responsive cellular pathways that signal host defense and control infection outcome in vivo. Aim 2 studies will define the viral genetic elements within NS3/4A and NS5A that impart regulation of host defense signaling and IRF function in vivo. This work will feature the use of an NS3 protease inhibitor and IFN therapy applications to determine how therapeutic modulation of the NS3/4A or NS5A blockades to host defense affect the host response to infection. Aim 3 studies will comprise in vitro approaches for pathway validation and gene function analysis to define the antiviral effector pathways and genes of the host response that control HCV and/or HIV/HCV RNA replication and infection. Perfomance Sites University of Washington, Seattle, WA with subcontract to University of Alberta, Edmonton, Alberta, Canada Principal Investigator/ProgramDirector (Last, First, Middle): GALE, Michael J., DETAILED BUDGET FOR INITIAL BUDGET PERIOD DIRECT COSTS ONLY